Injection Device

ABSTRACT

An injection device for injection of set doses of medicine from a cartridge has a nut that is screwed up along a threaded piston rod during a dose setting operation. The nut is screwed along the piston rod by rotating a dose setting member. A rotational coupling mechanism includes an axially displaceable coupling member which is rotated as a function of axial displacement. During dose setting, the nut is allowed to rotate relative to the coupling member. During injection, the coupling member is rotationally locked to the nut. This provides a dose setting and injection mechanism wherein the nut member is both rotated during dose setting and during injection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of copending U.S. application Ser.No. 11/911,871 filed Oct. 18, 2007 which is a 35 U.S.C. §371 nationalstage application of International Patent Application PCT/EP2006/061748(published as WO 2006/114396), filed Apr. 21, 2006, which claimedpriority of Danish Patent Application PA 2005 00589, filed Apr. 24,2005; this application further claims priority under 35 U.S.C. §119 ofU.S. Provisional Application 60/676,713, filed May 2, 2005.

The present invention relates to syringes having a piston drive elementfor engaging and moving a piston within a medication cartridge, by whicha dose can be set by rotating a nut along the piston drive elementduring dose setting, and wherein a set dose can be expelled by drivingthe nut to its initial position.

BACKGROUND OF THE INVENTION

An almost classic pen which adopts the above described dose setting andinjecting scheme is described in EP 327 910.

By setting a dose on this pen a tubular member forming an injectionbutton is screwed up along a threaded piston rod a distancecorresponding to the distance said piston rod must be moved to injectthe set dose. The tubular member simply forms a nut which is during thedose setting screwed away form a stop and which is during the injectionpressed back to abutment with said stop and the force exerted on thebutton is directly transmitted to the a piston closing one end of anampoule in the syringe which ampoule contains the medicament to beinjected. When the piston is pressed into the ampoule the medicament ispressed out through a needle mounted through a closure at the other endof the ampoule.

By time it has been wanted to store larger amount in the ampoules,typically 3 ml instead of 1.5 ml. As it has not been appropriate to makethe syringe longer the ampoule is instead given a larger diameter, i.e.the area of the piston facing the medicament in the ampoule has beendoubled and consequently the force which has to be exerted on the pistonto provide the same pressure as previously inside the ampoule has beendoubled. Further the distance the piston has to be moved to inject oneunit of the medicament has been halved.

This development is not quite favourable, as especially users havingreduced finger strength have their difficulties in pressing theinjection button, a problem that is further increased when still thinnerneedles are used to reduce the pain by injection. Also with quite smallmovements of the button it is difficult to feel whether the button ismoved at all and by injection of one unit from a 3 ml ampoule the pistonand consequently the injection button has to be moved only about 0.1 mm.

Consequently a wish for a gearing between the injection button and thepiston has occurred so that the button has a larger stroke than has thepiston. By such a gearing the movement of the injection button is madelarger and the force, which has to be exerted on the injection button,is correspondingly reduced.

In EP 608 343 a gearing is obtained by the fact that a dose settingelement is screwed up along a spindle having a thread with a high pitch.When said dose setting element is pressed back in its axial directionthe thread will induce a rotation of said dose setting element, whichrotation is via a coupling transmitted to a driver nut with a fine pitchwhich driver nut will force a threaded not rotatable piston rod forward.

A similar gearing is provided in WO 99/38554 wherein the thread with thehigh pitch is cut in the outer surface of a dose setting member and isengaged by a mating thread on the inner side of the cylindrical housing.However, by this kind of gearing relative large surfaces are slidingover each other so that most of the transformed force is lost due tofriction between the sliding surfaces. Therefore a traditional gearingusing mutual engaging gear wheels and racks is preferred.

From WO 96/26754 is known an injection device wherein two integratedgear wheels engages a rack fixed in the housing and a rack inside aplunger, respectively. When the plunger is moved axially in the housingthe rack inside this plunger can drive the first gear wheel to make theother integral gear wheel move along the fixed rack in the housing.Thereby the gear wheel is moved in the direction of the plunger movementbut a shorter distance than is this plunger and this axial movement ofthe integrated gear wheels is via a housing encompassing said gearwheels transmitted to a piston rod which presses the piston of anampoule further into this ampoule. However, the rack inside the plungeris one of a number axial racks provided inside said plunger. These racksalternates with untoothed recesses, which allow axial movement of theplunger without the first gear wheel being in engagement with a rack inthis plunger. This arrangement is provided to allow the plunger to bemoved in a direction out of the housing when a dose is set. When theplunger is rotated to set a dose it is moved outward a distancecorresponding to one unit during the part of the rotation where thefirst gear wheel passes the untoothed recess, thereafter the first gearwheel engages one of the racks so the set unit can be injected, or therotation can be continued to make the first gear wheel pass the nextrecess during which passing the set dose is increased by one more unitand so on until a dose with the wanted number of units is set.

A disadvantage by this construction is that the teeth of the racks andgearwheels alternating have to be brought in and out of engagement witheach other with the inherit danger of clashing. As only a few racksseparated by intermediary untoothed recess can be placed along the innersurface of the plunger only few increments can be made during a 360°rotation.

In U.S. Pat. No. 6,663,602 is disclosed an injection device, wherein adirect gearing, i.e. a gearing by which more transformations ofrotational movement to linear movement and linear movement to rotationalmovement are avoided, between the injection button and the piston rod.

The injection device shown in U.S. Pat. No. 6,663,602 comprises ahousing wherein a piston rod threaded with a first pitch is nonrotatable but longitudinally displaceable guided, a nut engaging thethread of the piston rod which nut can be screwed along the threadedpiston rod away from a defined position in the housing to set a dose andcan be pressed back to said defined position carrying the piston rodwith it when the set dose is injected, a dose setting member which canbe screwed outward in the housing along a thread with a second pitch tolift an injection button with it up from the proximal end of thehousing. This injection device is provided with a gearbox which providesa gearing between the axial movements of the injection button and thenut relative to the housing which gearing has a gearing ratiocorresponding to the ratio of said second and first pitch.

Although broadly being considered state of the art, the injection devicedisclosed in U.S. Pat. No. 6,663,602 presents important mechanicalconstraints due to the construction principle of the linear gearingsystem which acts during dosing. According to the injection device ofU.S. Pat. No. 6,663,602, the length of the nut/piston rod assembly isincreased during the dose setting by rotating the nut in a thread on thepiston rod. During dosing, the linear displacement of the nut and theinjection button are coupled such that there is proportionality betweenthe movement of the nut and the injection button, the proportionalitygiven by the transmission ratio of the gear box. As the nut isrotationally confined relatively to the piston rod during dosing, thetranslation of the nut corresponds to the translation of the piston rodand thus ultimately to the dose of medication administered.

As the gear is an integrated part of the construction and as the gearcan only be designed to certain transmission ratios, the gear impliesimportant constraints on the obtainable ratio of movement of theinjection button relative to the movement of the piston. Due to thedirect proportionality between the movement of the piston rod and theadministered dose of medication, the same syringe can not easily beadapted to different medications. Although adaptation is possible bychanging the transmission ratio of the linear gear, this solution willin general be very complex and imply a complete redesign of the syringe.

DISCLOSURE OF THE INVENTION

The injection devices disclosed in U.S. Pat. No. 6,663,602 comprisesdose setting and injection mechanisms wherein the nut is heldrotationally fixed during dose delivery. However, according to thepresent invention, the nut may be rotated relative to the housing, alsoduring dose delivery.

According to one aspect of the present invention, the injection devicecomprises:

a. a housing for a dose setting and injecting mechanism, the housinghaving a proximal end and a distal end,b. a rotatable dose setting member,c. an axially displaceable piston rod having a first thread and anadditional longitudinally extending track,d. a central opening in the housing for engaging the additionallongitudinally extending track of the piston rod, thus guiding theangular movement of the piston rod during axial translation of thepiston rod,e. a threaded nut engaging the first thread of the piston rod, the nutbeing rotatably locked to the dose setting member during dose setting,f. a rotational coupling mechanism having a coupling member which isaxially displaceable from a first position to a second position, therotational coupling mechanism allowing rotational movement of the nutrelative to the coupling member during dose setting while preventingrotational movement during injection. The coupling member isrotationally coupled to the housing so as to be urged to rotate as afunction of axial displacement of the coupling member relative to thehousing during at least a part of the axial displacement from said firstto said second position.

According to such a configuration, a prolongation or reduction of thestroke of the injection button compared to the stroke of the piston rodmay be obtained. Further, as this configuration implies a change in therate of rotation of the dose setting member for a given dose to beinjected, a dose scale reading with a different layout may be obtained.In this way, a scale reading with increased distance between consecutivenumbers may be obtained, which provides the possibility of increasingthe font size of the labels of the scale reading. Also, thisconfiguration provides the possibility of fine tuning the gearing ratio,if the injection device is so configured.

According to a second aspect of the invention, the dose setting memberis axially displaceable as a result of rotation of the dose settingmember relative to the housing, while the coupling member is coupled tothe dose setting member such that axial displacement of the dose settingmember substantially corresponds to axial displacement of the couplingmember.

According to a third aspect of the invention, the coupling member has athread and is threadedly engaged with a helical thread disposed in thehousing, the thread of the housing having a constant pitch. According tothis aspect, a particularly simple solution is obtained.

According to a fourth aspect of the invention, the coupling member has athread which engage a longitudinally extending track disposed in thehousing wherein the longitudinally extending track has a variable pitchalong the extension of the track. According to this aspect, the rotationof the dose setting member is nonlinear with respect to the variousspecific dose selections. Thus, a dose setting member with a nonlinearscale is obtainable, e.g. a scale can be provided having comparablelarger steps for smaller doses to be injected than for larger doses.This implies improved resolution in the low range of injectable doses.Also, an injection button can be provided having a stroke that isnonlinear with respect to the specific amount of drug to be injected,e.g. having a prolonged stroke for smaller doses compared to thesolutions provided for in U.S. Pat. No. 6,663,602.

According to a fifth aspect of the invention, the rotational couplingmechanism comprises an incremental feedback mechanism providingincremental clicks during dose setting corresponding to dose volume.This aspect provides an easy adjustment of the rotational movement ofthe dose setting drum for each click, relatively to the housing part. Incombination with the third aspect, an increase or a decrease of distancebetween the numbers on the dose setting drum or dose setting scale andthus the rotation for each click can be varied by choosing a specificpitch of the thread of the housing which engages the thread of thecoupling member. By varying the inclination of the track along theextension of the track, it is possible to vary the rotation per click ina nonlinear way.

According to a sixth aspect of the invention, an injection button isoperatively connected to a gear box assembly coupling axial movement ofthe injection button with axial movement of the nut. A gearing betweenthe movements of the injection button and the nut may be obtained by thegearbox comprising at least one gear wheel carried by a connector whichprojects from the gear box longitudinally displaceable but non rotatablerelative to said gearbox and is integral with the nut, a first rackintegral with a first element of the gearbox, which element isrotational but not longitudinally displaceable relative to the housing,and second element carrying a second rack projecting from said gearboxlongitudinally displaceable but non rotatable relative to said firstelement and being coupled to the injection button to follow longitudinalmovements of said button, the at least one gear wheel engaging the firstand the second rack, respectively, and being dimensioned to provide agearing by which a longitudinal movement of the second rack istransformed to a longitudinal movement of the connector with a gearingratio for the mentioned longitudinal movements of the second rack andthe connector relative to the housing, which gearing ratio substantiallycorresponds to the ratio of said second to said first pitch.

In such a device only the forces necessary to drive the dose settingmember are transformed by a thread with a high pitch whereas the forcesnecessary to move the piston by injection is transmitted to said pistonthrough a conventional gear with constantly engaging gears and racks.

In a seventh aspect of the invention, the piston rod is provided with astop for the movement of the nut along the thread of said piston rod,thereby forming an end-of-content stop. This way a dose setting limiteris provided in the classic way, which involves no additional members toprevent setting of a dose exceeding the amount of liquid left in theampoule.

According to an eighth aspect of the invention, the additionallongitudinally extending track on the piston rod is helically disposedon the external surface of the piston rod thereby forming a secondthread on the piston rod. By forming this track in a helical fashion,the piston rod is rotated as a result of axial displacement of thepiston rod relative to the housing. By rotating the piston rod and thecoupling member a similar angle during dosing, it is possible to setsmaller or bigger dose volume per click, and still have an EOC(End-Of-Content) stop between the piston rod and the nut.

As used herein, the term “drug delivery device” according to the instantinvention shall mean a single-dose or multi-dose, disposable orre-useable device designed to dispense a selected dose of a medicinalproduct, preferably multiple selected doses, e.g. insulin, growthhormones, low molecular weight heparins, and their analogues and/orderivatives etc. Said device may be of any shape, e.g. compact orpen-type. Dose delivery may be provided through a mechanical (optionallymanual) or electrical drive mechanism or stored energy drive mechanism,such as a spring, etc. Dose selection may be provided through a manualmechanism or electronic mechanism. Additionally, said device may containcomponents designed to monitor physiological properties such as bloodglucose levels, etc. Furthermore, the said device may comprise a needleor may be needle-free. In particular, preferred embodiment the term drugdelivery device shall mean a disposable multi-dose pen-type devicehaving mechanical and manual dose delivery and dose selectionmechanisms, which is designed for regular use by persons without formalmedical training such as patients. Preferably, the drug delivery deviceis of the injector-type.

The term “housing” according to instant invention shall preferably meanan exterior housing (“main housing”, “body”, “shell”) or interiorhousing (“inner body”, “insert”) having internal and external threads.The housing may be designed to enable the safe, correct, and comfortablehandling of the drug delivery device or any of its mechanisms. Usually,it is designed to house, fix, protect, guide, and/or engage with any ofthe inner components of the drug delivery device (e.g., the drivemechanism, cartridge, plunger, piston rod) by limiting the exposure tocontaminants, such as liquid, dust, dirt etc. In general, the housingmay be unitary or a multipart component of tubular or non-tubular shape.Usually, the exterior housing serves to house a cartridge from which anumber of doses of a medicinal product may by dispensed. However, acartridge may be directly coupled to the housing so as to be partly orfully external to the housing.

The term “engaged” according to instant invention shall particularlymean the interlocking of two or more components of the drivemechanism/drug delivery device, e.g. a spline or thread connection,preferably the interlocking of helical threads of components(“threadedly engaged”). The term “engaged” encompasses the use ofintermediary components coupling threadedly engaged threads.

The term “thread” according to instant invention shall preferably mean afull or part thread, e.g., a cylindrical spiral rib/groove, usually ofhelical nature or comprising linear inclined parts, located on theinternal and/or external surface of a component of the drug deliverydevice (“internal thread” and/or “external thread”), having anessentially triangular or square or rounded section designed to allowcontinuous free rotational and/or axial movement between components.Optionally, a thread may be further designed to prevent rotational oraxial movement of certain components in one direction.

The term “dose setting member” according to instant invention shall meanan essentially tubular component of essentially circular cross-sectionhaving either: a) both an internal and external thread, or b) aninternal thread, or c) an external thread. The dose setting member maybe designed to indicate a selected dose of a dispensable product. Thismay be achieved by use of markings, symbols, numerals, etc., e.g.printed on the external surface of the dose setting member or anodometer, or the like. Also, a separate dose scale may be used, eithercomprising a mechanical or an electronic display.

The term “lead” according to instant invention shall preferably mean theaxial distance a nut would advance in one complete revolution;preferably “lead” shall mean the axial distance through which acomponent having a helical thread, i.e. dose setting member, nut, pistonrod, etc., of the drive mechanism travels during one rotation. Thereforelead is a function of the pitch of the thread of the relevant component.

The term “pitch” according to instant invention shall preferably meanthe distance between consecutive contours on a helical thread, measuredparallel to the axis of the helical thread.

The term “piston rod” according to instant invention shall mean acomponent adapted to operate through/within the housing, designed totranslate axial movement through/within the drug delivery device,preferably from the nut to the piston, for the purpose ofdischarging/dispensing an injectable product. Said piston rod may beflexible or not. It may be a simple rod, a lead-screw, or the like. The“piston rod” according to instant invention shall further mean acomponent having a non-circular cross-section and preferably having oneor more threads located partly or fully extending along its length. Itmay be made of any suitable material known by a person skilled in theart.

The term “incremental feedback mechanism” according to instant inventionshall mean a mechanism providing the dose setting to occur in a numberof discrete incremental steps, e.g. one incremental click for eachinternational unit being set, the incremental feedback mechanismpreferably providing a tactile or audible click which can be sensed orheard by a user operating the pen.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described in further details withreferences to the drawing, wherein

FIG. 1 schematically shows a sectional view of an injection deviceaccording to the invention, and

FIG. 2 shows schematically a sectional view of the gear box along theline I-I in FIG. 1,

FIG. 3 shows a longitudinal sectional view in the dose setting part ofanother embodiment of an injection device according to the invention,

FIG. 4 shows a longitudinal sectional view perpendicular to the view inFIG. 3,

FIG. 5 shows an exploded view of the of the device shown in FIGS. 3 and4,

FIG. 6 a shows a large scale view of the tubular part 105 of FIG. 5according to one embodiment of the invention, and

FIG. 6 b shows a large scale view of the corresponding part 105 of aprior art injection device.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The device shown in the appended drawings is shown as an injector pen,which pen has an elongated body with a central axis. However, otherforms are within the scope of the invention.

In the device shown in FIG. 1 an elongated cylindrical housing 1 has apartitioning wall 2 which divides the housing in a compartmentcontaining a dose setting mechanism and a compartment 3 designed for theaccommodation of a not shown ampoule. The partitioning wall 2 isprovided with an opening extending there through. Alternatively, thewall may be replaced by an insert which is secured against rotationaland axial motion with respect to the main structure of the housing 1,the opening being formed in said insert. A piston rod 4 having a firstthread 4 a and an additional longitudinally extending track 4 b formedin or on the piston rod 4, extends through the opening 2 b, which isprovided with one or more ribs which mates and engages the additionallongitudinal extending track 4 b.

In accordance with the specific design of the additional longitudinallyextending track 4 b and the mating opening 2 b in partition wall 2, thepiston rod 4 is rotationally guided as a function of axial displacementof the piston rod. To obtain a piston rod 4 which is longitudinallydisplaceable while being rotationally locked relative to the housing,the additional longitudinally extending track 4 b is formed as arectilinear track which extends parallel to the axis of the piston rod4. Alternatively, to obtain a piston rod 4 which is being rotated as afunction of axial displacement of the piston rod 4, the additionallongitudinal track 4 b is formed as a helical groove or thread whichmates and engages with helical ribs or threads formed in opening 2 b inthe partition wall 2.

In accordance with the specific design of the injection device, thefirst thread 4 a and the additional longitudinally extending track 4 bmay be disposed on opposite ends of the piston rod 4, may be partlyoverlapping or fully overlapping in the axial direction of the pistonrod 4. Furthermore, the thread 4 a may be disposed with a larger depththan the additional longitudinally extending track 4 b or vice versa. InFIG. 1, the threads 4 a and 4 b and the threaded opening 2 b areschematically represented.

Concentrically with the housing 1 the wall 2 carries on its side turningaway from the compartment 3 a tubular element 5 which is at a part of itadjacent to the wall 2 provided with an outer thread 6 and which has atits free end a circumferential recess 7. A ring shaped coupling element8 on a gear box 9 engages the recess 7. By this coupling the gearbox isfixed in the housing 1 in a way that allows the gearbox 9 to rotate inthe housing but not to be axially displaced relative to said housing.

In the gearbox 9 a gear wheel assembly comprising two integral gearwheels is journaled on a shaft 11, which runs perpendicular to thelongitudinal axis of the device between two axial connection bars 12.The connection bars 12 project from the gear box towards the partitionwall 2 and are connected to a nut 13 which engages the first thread 4 aof the piston rod 4. The gear wheel assembly comprises a gear wheel 14with a large diameter engaging the teeth of a rack 15 which is guided inthe gear box to be displaced in the longitudinal direction of thedevice, and a gear wheel 16 with a small diameter engaging a rack 10 inFIG. 2 extending in the longitudinal direction of the device on theinner wall of the gearbox 9. The gear wheel 16 with the small diametermay be divided into two gear wheels placed on each side of the of thegear wheel 14, and the rack on the inner wall of the gearbox 9 may havea longitudinal recess without any teeth to make room for the gear wheel14.

A tubular dose setting member 17 fitting into the housing 2 is at an endprovided with an internal thread mating and engaging the outer thread 6of the tubular element 5 and has at its other end a part with enlargeddiameter forming a dose setting button 18. Due to the engagement withthe thread 6 the dose setting member 17 may be screwed in and out of thehousing to show a number on a not shown helical scale on its outersurface in a not shown window in the housing 1.

A bottom 19 in a deep cup shaped element, which has a tubular part 20fitting into the dose setting member 17 and encompassing the gearbox 9,forms an injection button. Coupling means between the dose settingmember 17 and the cup shaped element ensures that rotation of the dosesetting member 17 is transmitted to the cup shaped element. Further theinner wall of the tubular part 20 has longitudinal recesses 22 engagedby protrusions 23 on the gearbox 9 so that rotation of the dose settingmember 17 via the cup shaped element is transmitted to the gearbox 9.

At the edge of the open end of the cup shaped element a rosette ofV-shaped teeth are provided, which teeth engage a corresponding rosetteof V-shaped teeth 24 on a coupling member 25 which is pressed againstthe edge of the cup shaped element by a spring 26 which is compressedbetween a not toothed side of the coupling member 25 and a round goingshoulder 27 on the inner wall of the dose setting member 17 at an innerend of the inner thread of this member. The coupling member 25 isprovided with one or more inner protrusions forming a thread 28, whichis engaged by a thread or track 37 on the tubular element 5 so that thecoupling member 25 will be forced to rotate when it is displaced axiallyrelative to the housing. The track 37 may be designed as a helicalthread with a constant pitch along the extension of the track.Alternatively, the layout of the pitch may be formed with a variablepitch along the extension of the track, e.g. by forming a track withinclined as well non-inclined rectilinear steps, or curved parts.

The track 37 is so shaped that the dose setting member 17 rotatesrelative to the coupling member 25, when a user dials a dose by rotatingthe dose setting button 18. In this way a click coupling is establishedwhich makes a click noise when the V-shaped teeth at the edge of the cupshaped element by rotation of this element rides over the V-shaped teethof the coupling member 25, i.e. an incremental feedback mechanism isprovided.

A head 29 on the projecting end of the rack 15 is with a play fixed atthe bottom of the cup shaped element between the bottom 19 forming theinjection button and an inner wall 30 near this bottom. The rack isfixed in a position with its head pressed against the wall 30 by aspring 31 between the bottom 19 and the head 29.

To set a dose the dose setting button 18 is rotated to advance thedose-setting member 17 in the proximal direction in accordance with thethread 6. Due to the coupling 21 the cup shaped element will follow therotation of the dose-setting member 17 and will be lifted concurrentlywith this member up from the end of the housing 1. During dose setting,the respective amount of axial displacement of the dose setting member17 and the injection button 19 depends on the pitch of the thread 6, thepitch of the first thread on the piston rod 4 and the gear ratio. Also,if the piston rod 4 is allowed to move during dose setting, the axialand rotational movement of the piston rod 4 influences the amount thatthe injection button will be displaced. By the rotation of the cupshaped element the V-shaped teeth 24 at the edge of its open end willride over the V-shaped teeth of the coupling member 25 to make a clicksound for each unit the dose is changed. A too high set dose can bereduced by rotating the dose setting button 18 in the opposite directionof the direction for increasing the dose. When the dose setting memberis screwed along the thread 6 on the tubular element 5, the couplingmember 25 will follow the dose setting member in its axial movement asthe spring 26 is supported on the shoulder 27.

The spring will keep the V-shaped teeth of the coupling member 25 andthe cup shaped element in engagement and maintain in engagement thecoupling 21, which may comprise Δ-shaped protrusions 32 on the cupshaped element engaging Λ-shaped recesses in an inner ring 33 in thedose setting button 18.

Due to the axial displacement of the dose setting member 17 during dosesetting, the coupling member 25 is axially displaced as well. Accordingto the specific design of the threads or tracks 28 and 37, the couplingmember 25 is forced to rotate as the coupling member 25 is axiallydisplaced. In some embodiments, the thread 37 is formed as a helicalthread which has a constant pitch along the length of the total axialdistance that the coupling member is allowed to move. Depending on thedirection of rotation of track 37, the dose setting button 18 has to berotated a larger or smaller angle for each click to occur compared to asituation where the coupling member is kept rotationally fixed. Acorresponding amendment of the layout of the scale reading may beprovided, e.g. by forming the dose scale with larger or smaller spacesbetween neighboring dose values.

The rotation of the dose setting button 18 and the cup shaped element isfurther transmitted to the gearbox 9 through the protrusions 23 on thisgearbox engaging the longitudinal recesses 22 in the inner wall of thetubular part 20 of said cup shaped element. The rotation of the gearbox9 is through the connection bars 12 transmitted to the nut 13, which inthis way is advanced along the first thread 4 a of the piston rod 4 andlifted away from its abutment with the wall 2 when a dose it set. As thedose is set by moving the nut 13 on the piston rod which operates thepiston in the not shown ampoule in the compartment 3, a dose settinglimiter, which ensures that the size of the set dose does not exceed theamount of medicament left in the ampoule, can easily be established byproviding the piston rod 4 with a stop 35 which limits the movement ofthe nut 13 up along the piston rod 4.

Due to the confinement of the head 29 in the space between the bottom 19and the wall 30 of the cup shaped element, the rack 15 is drawn with theinjection button outward. Depending on the specific gear ratio of thegear assembly, the outward movement of the rack 15 corresponds to anoutward movement of nut 13. As the nut 13 is rotated during dosesetting, the length of the piston rod/nut assembly is prolonged,depending on the mutual pitch of the piston rod/nut threads anddepending on the actual design of the additional longitudinallyextending track 4 b.

By varying the pitch of the different threads or the gear ratio, thepiston rod is either moved distally, proximally or held stationaryduring dose setting.

Ideally, if no axial movement of the piston rod 4 is wanted during dosesetting the pitch of the thread 6 and the thread formed in the pistonrod 4 a as well as the pitch of the outer recess (6) should be matchedexactly to the gearing ratio of the gear box depicted in FIG. 2.

However, tolerances in the machining of the components comprising thepen may lead to a slight unintended mismatch of the pitches relativelyto the transmission ratio of the gearbox 9. Especially the situationwhere the piston rod 4 advances slightly during dose setting is highlyundesirable as the injection device during dose setting will expel asmall amount of medication.

This situation is avoided by mismatching one or more of the abovementioned pitches to the transmission ratio of the gearbox such that thepiston rod 4 is slightly withdrawn during dose setting. The mismatch ofpitches is most simply implemented by modification of the pitch of therecess 4 a made in the piston rod 4 and the corresponding thread in thenut 13. In addition, if the additional longitudinally extending track 4b on piston rod forms a helical thread, i.e. allowing the piston rod 4to rotate with respect to the housing (1), this threaded connection hasto be taken into account when designing the mechanism.

Alternatively, the injection device is designed such that the recess inthe piston rod is initially designed to be axially aligned with thepiston rod. On assembled production prototypes the advance of the pistonrod during dose setting is measured. Hereafter the axial aligned recessis redesigned to a helical recess where the superimposed rotation of thepiston rod during dose setting compensates for the tolerances in themachining.

According to one embodiment of the invention the pitches of the threadedparts and the linear gearing are matched such that the piston rodretracts between 0% and 2% of the full linear translation relatively tothe cartridge during dose setting.

A corresponding solution can be provided in the injection device shownin U.S. Pat. No. 6,663,602 which contains an injection device having acoupling member 25, which is kept rotationally locked with respect tothe housing. For that particular injection device, a slight mismatch ofeither the thread 6 or the thread of piston rod 4 to the transmissionratio of the gearbox can be provided such that the piston rod 4 isslightly withdrawn during dose setting.

In the device according to the instant invention, to inject a set dosethe injection button is pressed by pressing on the bottom 19. In theinitial phase of the pressing, the spring 31 is compressed where afterthe pressing force is directly transmitted to the head 29 of the rack 15and this way to the rack 15 itself. Through the gear box 9 the force istransformed and is transmitted through the connection bars 12 to the nut13 which will press the piston rod 4 into the compartment 3 until thedose-setting member 17 abuts the wall 2.

During the initial phase of the movement of the injection button theΔ-shaped protrusions 32 on the cup shaped element will be drawn out oftheir engagement with the Λ-shaped recesses in the ring 33. Thedose-setting member 17 can now rotate relative to the injection buttonand will do so when the Δ-shaped protrusions 32 press against a shoulder34 at the bottom of the dose setting button 18. Only a force sufficientto make the dose setting member rotate to screw itself downward alongthe thread 6 is necessary as the force necessary to make the injectionis transmitted to the piston rod 4 through the gearbox 9. A helicalreset spring 36 concentric with the dose setting member can be mountedat the lower end of this member and can have one end anchored in thedose setting member 17 and the other end anchored in the wall 2. Duringsetting of a dose this spring may be tighter coiled so that on the dosesetting member it exerts a torque approximately corresponding to thetorque necessary to overcome the friction in the movement of the dosesetting member along the thread 6 so that the force which the user haveto exert on the injection button is only the force necessary to drivethe piston rod into an ampoule to inject the set dose.

It shall be noticed that use of only one size gear wheel which engagesas well the rack 15, which is movable relative to the gear box 9, as therack 10, which is unmovable relative to the gear box, provides a gearingratio of 2:1 for the longitudinal movement relative to the syringehousing 1 for the movable rack 15 and the connector 12, which carriesthe shaft 11 of the gear wheel.

FIGS. 3 and 4 shows an embodiment wherein only one size gear wheel isused and wherein elements corresponding to elements in FIGS. 1 and 2 aregiven the same references as these elements with a prefixed “1”.

For manufacturing reasons minor changes are made. So the partitioningwall 102 and the tubular element 105 are made as two parts which are bythe assembling of the device connected to each other to make theassembled parts act as one integral part. The same way the dose settingmember 117 and the dose setting button 118 are made as two parts, whichare fixed firmly together.

A circumferential recess 107 is provided as an outer recess at the freeend of the tubular part 105 and a ring shaped coupling element isprovided as an inner bead 108 on the gearbox element 109 which beadengages the recess 107 to provide a rotatable but not axiallydisplaceable connection between the tubular part 105 and the gearbox.

A tubular element 120 having ridges 122 which engages recesses 123 onthe gearbox is at its upper end closed by a button 119 from which aforce provided by pressing this button is transmitted to the tubularelement 120.

The gearbox is formed by two shells, which together form a cylinderfitting into the tubular element where the shells are guided by theengagement between the ridges 122 and the recesses 123. Racks 110 and115 are provided along edges of the shells facing each other. One shellforming the gearbox part 109 is provided with the inner bead 108, whichengages the circumferential recess 107 at the end of the central tubularpart 105 and carries the rack 110. The other shell is axiallydisplaceable in the tubular element 120 and forms the rack 115. At itsouter end projecting from the gearbox the shell carrying the rack 115 isprovided with a flange 140 which is positioned in a cut out 141 in theend of the tubular element 120 carrying the button 119 so that thisbutton and the tubular element 120 can be moved so far inward in thedevice that the engagement of the teeth 132 and 133 can be releasedbefore the button 119 abuts the flange 140.

A tubular connection element 112 connects the threaded piston rod 104with the gearbox. At its end engaging the piston rod 104 the connectionelement has a nut 113 with an internal thread mating the external thread104 a of the piston rod 104. At its end engaging the gear box theconnection element is provided with two pins 111 projectingperpendicular to the longitudinal axis of the connection element 112 ateach side of this element. Each pin 111 carries a gear wheel 114 whichis placed between and engages the two racks 110 and 115. This way theconnection element 112 will be rotated with the gear box but can bedisplaced axially relative to said gear box when the racks 110 and 115are moved relative to each other. In practice it will be the rack 115,which is moved relative to the gearbox element 109 and the housing 1 andwill by the shown construction result in a movement of the connectionelement 112 relative to housing a distance which is half the distancewhich the rack 115 is moved. A coupling member 125 which is at itsperiphery provided with a rosette of teeth 124 and has a central borefitting over the central tube in the housing 101 so that this couplingmember 125 can be axially displaced along said central tube 105. One ormore internal protrusions 128 on the central bore of the coupling member125 is shown in FIGS. 3 and 4. The protrusions engage mating helicalrecessed tracks or threads 137 (not shown in FIGS. 3 and 4) in thecentral tube to make the coupling member 125 confined with respect torotational movements, that is, the coupling member 125 being angularlymoved in accordance with the axial displacement of the coupling member125 along the tracks or threads 137. Due to this rotational confinementor rotational guiding in the housing, a rosette of teeth at the edge ofthe tubular element 120 can click over the teeth 124 of the couplingmember when said tubular element is rotated together with the dosesetting member 117. A spring 126 working between the coupling member 125and an internal shoulder 127 provided in the dose setting member 117makes the coupling member follow the tubular element 120 when thiselement with the dose setting member is moved longitudinally in thehousing. To make the dose setting member easy rotatable, especially whensaid dose setting member is pressed inward in the housing, a rollerbearing having an outer ring 142 supported by the shoulder 127 and aninner ring 143 supporting a pressure bushing 144 which supports thespring 126. By the provision of this smooth running support only verysmall axial forces are needed to rotate the dose setting member 117 backto its zero position when a set dose is injected. This solution replacesthe provision of a reset spring as the spring 36 in FIG. 1. The bearingis shown as a radial bearing but can be replaced by an axial bearing.

Whereas the track 137 is not shown in FIGS. 3 and 4, this track can beviewed in FIG. 5 which depicts an exploded view of the embodiment shownin FIGS. 3 and 4. The central tubular part 105 is further shown in agreater scale in FIG. 6 a while FIG. 6 b the corresponding part of priorart injection shown in U.S. Pat. No. 6,663,602.

Table 1 is a list showing different configurations of theabove-described injection device. In table 1, configuration no. 1corresponds to the device which is disclosed in U.S. Pat. No. 6,663,602,i.e. a device having a piston rod that is non-rotational but axiallydisplaceable and having a track 37, 137 which is a rectilinear trackwhich extends parallel to the axis of the injection device.

Configurations no. 2-6 correspond to embodiments having the same pitchof the threads 6, 106 on the dose setting member and the first thread 4a, 104 a on the piston rod as in configuration no. 1. In configurationno. 2-6, the track 37, 137 is formed as a helical track having aconstant pitch along the extension of the track, each of theconfigurations corresponding to specific pitches of the track.Configurations 1-4 have a piston rod that is non-rotational but axiallydisplaceable. Configurations no. 5 and 6 has a helical track 4 b, 104 bwhich mates and engages the threaded opening 2 b in the housing.

TABLE 1 Pitch of dose Pitch (28, 128) on setting member coupling memberPitch of piston rod Pitch of piston rod relative to housing relative tohousing relative to nut (13, 113) relative to housing First pitch (6,106) Second pitch on the First pitch (4a, 104a) Second pitch (4b, 104b)Configuration on the tubular part tubular part (37, 137) on the pistonrod on the piston rod 1 7.2 0 3.6 0 2 7.2 −14.4 3.6 0 3 7.2 −7.2 3.6 0 47.2 14.4 3.6 0 5 7.2 −7.2 3.6 −3.6 6 7.2 −14.4 3.6 −7.2 (Positive pitchvalues indicates left handed threads, negative pitch values indicatesright handed threads, 0 (Zero) indicates a non rotational longitudinallytrack).

TABLE 2 Output Output Input Relative rotation between the Deliveredaxial dis- Rotation of the dose dose setting member and the placement ofthe Example setting member (17, 117) coupling member (25, 125) pistonrod (4, 104) # Configuration (in degrees) (in degrees) (in mm) 1 1 15 150.15 2 2 10 15 0.15 3 3 7.5 15 0.15 4 3 15 30 0.3 5 4 30 15 0.15 6 5 7.515 0.075 7 6 10 15 0.1

Table 2 lists examples with different dose settings for theconfigurations 1-6 wherein the third column of table 2 shows the angularamount that the dose setting drum 17, 117 has been dialed. Correspondingrotational movement of the dose setting drum relative to the couplingmember 25, 125 is listed in column 4 and the resulting axialdisplacement of the piston rod is listed in column 5.

Comparing examples 1-3 and 5 in table 2, it becomes clear that variationof the pitch of track 37, 137 changes the amount of the rotation thatthe dose setting member has to be dialed in order to expel a desireddose. Thereby an easy adjustment method is provided where the amountthat the dose setting member has to be rotated for advancing the dosesetting button one click, can be altered. Also, this provides thepossibility of changing the angular distance between consecutive numberson the dose scale. Hence, to obtain a dose scale layout with enlargedfont size or, alternatively, a decreased font size, the pitch of thetrack 37, 137 is chosen in accordance herewith.

Comparing example 3 and 6, it is readily apparent that introducing athreaded coupling between the piston rod and the housing, i.e. makingthe piston rod rotatable with respect to the housing, provides for thepossibility of obtaining an injection device with altered dosingamounts, e.g. a half-increment injection device.

When introducing a coupling member 25, 125 that rotates relative to thehousing, the end-of-content mechanism as described above may not work inan optimal way. However, by choosing the same pitch for the additionallongitudinally extending track 4 b, 104 b on the piston rod as for thepitch of the track 37, 137 it is ensured that the end-of-contentlimitation that the user may experience when setting a dose forinjection, corresponds to the exact amount that will be expelled duringdosing. In this way, a cartridge may be fully emptied when injecting thedose which corresponds to the end-of-content setting, i.e. the situationwhere the piston rod 4, 104 is fully retracted relative to the nut 13,113,

In further embodiments, the track 37, 137 may be designed to have avarying pitch along the track, i.e. having linear parts with inclined ornon-inclined stretches as well as curved stretches. Also, the rotationaldirection of the track may be changed from one part of the track toanother part of the track. One specific embodiment may be designed forlarger relative dose button movements for small dose settings than fordose settings corresponding to large doses. Thereby it is ensured thatthe resolution for small dose settings is held at a comparative highlevel.

Although the above described embodiments show different specific gearboxassemblies, it is to be noted that, within the scope of the presentinvention, various other types of gearboxes can be used. Also, thefunctionality of the gearbox can be omitted while the injection devicestill being within the scope of the present invention.

In addition, alternative embodiments having a dose setting member whichis kept axially fixed during dose setting/dosing will be applicable withthe present invention and within the scope of the appended claims. Onenon-limiting embodiment comprises an additional slave member which isrotationally coupled to the dose setting member, and which can be usedfor inducing axial movement on the coupling member during dose setting.

Further, a frictional coupling may be provided instead of theabove-described incremental feedback mechanism, whereby doses may be setamong a continuous selection of dose amounts.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference in theirentirety and to the same extent as if each reference were individuallyand specifically indicated to be incorporated by reference and were setforth in its entirety herein (to the maximum extent permitted by law).

All headings and sub-headings are used herein for convenience only andshould not be construed as limiting the invention in any way.

The use of any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

The citation and incorporation of patent documents herein is done forconvenience only and does not reflect any view of the validity,patentability, and/or enforceability of such patent documents.

This invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw.

1. An injection device comprising: a. a housing for a dose setting andinjecting mechanism, the housing having a proximal end and a distal end,b. a rotatable dose setting member, c. an axially displaceable pistonrod having a first thread and an additional longitudinally extendingtrack, d. a central opening in the housing for engaging the additionallongitudinally extending track of the piston rod, thus guiding theangular movement of the piston rod during axial translation of thepiston rod, e. a threaded nut engaging the first thread of the pistonrod, the nut being rotatably locked to the dose setting member duringdose setting, f. a rotational coupling mechanism having a couplingmember which is axially displaceable from a first position to a secondposition, the rotational coupling mechanism allowing angular movement ofthe nut relative to the coupling member during dose setting whilepreventing angular movement between the nut and the coupling memberduring injection, wherein the coupling member is angularly coupled tothe housing so as to be forced to move angularly as a function of axialdisplacement of the coupling member relative to the housing during atleast a part of the axial displacement from said first to said secondposition.
 2. The injection device as defined in claim 1, wherein thedose setting member is axially displaceable as a result of rotation ofthe dose setting member relative to the housing, and that the couplingmember is so coupled to the dose setting member that axial displacementof the dose setting member substantially corresponds to axialdisplacement of the coupling member.
 3. The injection device as definedin claim 1, wherein the coupling member has a thread and is threadedlyengaged with a helical thread disposed in the housing, the thread of thehousing having a constant pitch.
 4. The injection device as defined inclaim 1, wherein the coupling member has a protrusion which mates andengages a longitudinally extending track disposed in the housing thelongitudinally extending track having a variable pitch along theextension of the track.
 5. The injection device as defined in claim 1,wherein the rotational coupling mechanism comprises an incrementalfeedback mechanism providing incremental clicks during dose settingcorresponding to dose volume.
 6. The injection device as defined inclaim 1, wherein the injection device further comprises an injectionbutton and a gear box assembly coupling axial movement of the injectionbutton with axial movement of the nut.
 7. The injection device asdefined in claim 6, wherein the gear box assembly provides a gearingcausing the nut to move a distance in the distal direction duringinjection that is less than the distance moved by the injection button.8. The injection device as defined in claim 1, wherein the additionallongitudinally extending track on the piston rod is helically disposedthereby forming a second thread on the piston rod.
 9. The injectiondevice as defined in claim 8, wherein the first thread and thelongitudinally extending track on the piston rod are oppositelydisposed.
 10. The injection device as defined in claim 8, wherein thecoupling member has a thread and is threadedly engaged with a helicalthread disposed in the housing, the thread of the housing having aconstant pitch substantially corresponding to the pitch of theadditional longitudinally extending track on the piston rod.
 11. Theinjection device as defined in claim 2, wherein the coupling member hasa thread and is threadedly engaged with a helical thread disposed in thehousing, the thread of the housing having a constant pitch.
 12. Theinjection device as defined in claim 2, wherein the coupling member hasa protrusion which mates and engages a longitudinally extending trackdisposed in the housing the longitudinally extending track having avariable pitch along the extension of the track.
 13. The injectiondevice as defined in claim 9, wherein the coupling member has a threadand is threadedly engaged with a helical thread disposed in the housing,the thread of the housing having a constant pitch substantiallycorresponding to the pitch of the additional longitudinally extendingtrack on the piston rod.
 14. The injection device as defined in claim 2,wherein the rotational coupling mechanism comprises an incrementalfeedback mechanism providing incremental clicks during dose settingcorresponding to dose volume.
 15. The injection device as defined inclaim 3, wherein the rotational coupling mechanism comprises anincremental feedback mechanism providing incremental clicks during dosesetting corresponding to dose volume.
 16. The injection device asdefined in claim 4, wherein the rotational coupling mechanism comprisesan incremental feedback mechanism providing incremental clicks duringdose setting corresponding to dose volume.
 17. The injection device asdefined in claim 2, wherein the injection device further comprises aninjection button and a gear box assembly coupling axial movement of theinjection button with axial movement of the nut.
 18. The injectiondevice as defined in claim 3, wherein the injection device furthercomprises an injection button and a gear box assembly coupling axialmovement of the injection button with axial movement of the nut.
 19. Theinjection device as defined in claim 4, wherein the injection devicefurther comprises an injection button and a gear box assembly couplingaxial movement of the injection button with axial movement of the nut.20. The injection device as defined in claim 5, wherein the injectiondevice further comprises an injection button and a gear box assemblycoupling axial movement of the injection button with axial movement ofthe nut.
 21. The injection device as defined in claim 6, wherein theinjection device further comprises an injection button and a gear boxassembly coupling axial movement of the injection button with axialmovement of the nut.